rust-index: implementation of __getitem__
Although the removed panic tends to prove if the full test suite
did pass that the case when the input is a node id does not happen,
it is best not to remove it right now.
Raising IndexError is crucial for iteration on the index to stop,
given the default CPython sequence iterator, see for instance
https://github.com/zpoint/CPython-Internals/blobs/master/BasicObject/iter/iter.md
This was spotted by `test-rust-ancestors.py`, which does simple interations on
indexes (as preflight checks).
In `revlog.c`, `index_getitem` defaults to `index_get` when called
on revision numbers, which does raise `IndexError` with the same message as
the one we are introducing here.
BasedOnStyle: LLVM
IndentWidth: 8
UseTab: ForIndentation
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
AllowShortBlocksOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
IncludeCategories:
- Regex: '^<'
Priority: 1
- Regex: '^"'
Priority: 2